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RESEARCH PRODUCT

A geological field trip to the Côte d'Ivoire-Ghana transform margin

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Abstract During the Equanaute survey (June 1992), fourteen submersible dives were performed between 4950 and 2250 m water depths across the southern slope of the Cote d'Ivoire-Ghana Marginal Ridge (CIGMR), in the eastern Equatorial Atlantic. The CIGMR, a high-standing topographic marginal ridge along the Cote d'Ivoire-Ghana transform margin, is believed to result from a complex structural evolution due to the specific wrench-related rifting between Western Equatorial Africa and Northeastern Brazil, in Early Cretaceous times. In this paper we report and discuss geological observations made during dives, and sample analyses to resolve the lithology, paleoenvironmental conditions, age and origin of the CIGMR. The data help in better characterizing the different sedimentary and tectonic regimes which successively prevailed during the CIGMR formation and assessing the thermal regime operative during the fabrication and subsequent evolution of the margin. The thick sedimentary pile exposed along the southern CIGMR slope is made up of a repetitive clastic sequence indicative of a deltaic-to-prodeltaic environment. This sedimentary pile, of Early Cretaceous age, has recorded different stages of the transform margin structural evolution. 1. (1)|Syn- to post-lithification deformations first record extensional deformations related to the rifting of the adjacent northern divergent margin segment (the Deep Ivorian Basin). 2. (2)|Wrench tectonics has, at a later stage, produced intense fracturing and participated in local folding, chiefly detected upslope. The integrated studies of geological samples and in situ observations obtained during the Equanaute survey support models for transform margin evolution proposed mainly from geophysical data.